#include <iostream>
#include <vector>
using namespace std;

signed main()
{
    vector<int> v;
    int cnt[100000] = {0},n,a;
    cin>>n;
    for(int i=0;i<n;i++){
        cin>>a;
        if(cnt[a]==0)    v.push_back(a);
        cnt[a]++;
    }
    for(int i=0;i<v.size();i++){
        if(cnt[v[i]]==1){
            cout<<v[i];
            return 0;
        }
    }
    cout<<"None";
    return 0;
}
